Internal combustion engines use various types of filters in order to reduce overall engine component wear. In particular, a filter is used to remove much of the contaminant found in engine oil or created as part of engine operation. On certain diesel engines, two oil filters are used to improve the effectiveness of the filter on removing contaminant.
FIG. 1 shows a prior art system. In FIG. 1, a first filter 200 is located in the system such that the majority of the oil used to lubricate the moving parts passes through it. A second oil filter 202 is located just upstream of this first filter 200. The second oil filter 202 allows the remaining amount of oil to flow through it and directly into the engine oil reservoir (sump) 204. The second filter 202 is more efficient than the first filter 200, which also means that it is more restrictive to oil flow and acts to continuously clean the oil in the reservoir 204. The net effect is obtaining a higher cleanliness level in the oil without the impact of a high pressure drop across the first filter 200.
In certain prior art systems, the approach of FIG. 1 requires two separate filters 200, 202 installed in their own individual housings. This can be inconvenient, occupy too much space, and cause excessive use of housing materials. In these prior art systems, the second filter 202 is in parallel with the first filter 200 and is exposed to the same level of contaminant as the first filter 200. Further, these filters are often a part of a spin-on filter design. Improvements are desirable.